وَهَذَا كِتَابٌ أَنْزَلْنَاهُ مُبَارَكٌ فَاتَّبِعُوهُ وَاتَّقُوا لَعَلَّكُمْ تُرْحَمُونَ ﴿۱۵۵﴾ أَنْ تَقُولُوا إِنَّمَا أُنْزِلَ الْكِتَابُ عَلَى طَائِفَتَيْنِ مِنْ قَبْلِنَا وَإِنْ كُنَّا عَنْ دِرَاسَتِهِمْ لَغَافِلِينَ ﴿۱۵۶﴾ أَوْ تَقُولُوا لَوْ أَنَّا أُنْزِلَ عَلَيْنَا الْكِتَابُ لَكُنَّا أَهْدَى مِنْهُمْ فَقَدْ جَاءَكُمْ بَيِّنَةٌ مِنْ رَبِّكُمْ وَهُدًى وَرَحْمَةٌ فَمَنْ أَظْلَمُ مِمَّنْ كَذَّبَ بِآيَاتِ اللَّهِ وَصَدَفَ عَنْهَا سَنَجْزِي الَّذِينَ يَصْدِفُونَ عَنْ آيَاتِنَا سُوءَ الْعَذَابِ بِمَا كَانُوا يَصْدِفُونَ ﴿۱۵۷﴾

﴾155﴿ Wa haazaa Kitaabun anzalnaahu Mubaarakun fattabi'oohu wattaqoo la'al lakum turhamoon
﴾156﴿ An taqooloo inna maaa unzilal Kitaabu 'alaa taaa'ifataini min qablinaa wa in kunnaa 'an diraasatihim laghaafileen
﴾157﴿ Aw taqooloo law annaaa unzila 'alainal kitaabu lakunnaaa ahdaa minhum; faqad jaaa'akum baiyinatum mir Rabbikum wa hudanw wa rahmah; faman azlamu mimman kazzaba bi Aayaatil laahi wa sadafa 'anhaa; sanajzil lazeena yasdifoona 'an Aayaatinaa sooo'al 'azaabi bimaa kaanoo yasdifoon

﴾155﴿ And this Book which We have sent down is blessed, so follow it and be mindful (of Allah) so that mercy may be shown to you.
﴾156﴿ (And so that) you do not say, “The Books were only sent down to two groups before us, and indeed we were unaware of their reading.”
﴾157﴿ Or so that you do not say, “If a Book had been sent down to us, we would surely have been better guided than them.” Now there has come to you a clear proof from your Lord, and guidance, and mercy. So who is more unjust than one who denies the signs of Allah and turns away from them? Soon We will punish those who turn away from Our signs with the worst punishment, for having turned away.

[155] This verse is an encouragement toward the Qur’an by mentioning two qualities of the Book, two commands, and one underlying wisdom.
(Mubārak) — “blessed” — its explanation is found in verse 92 of this surah.
(Wa-ttaqū) — means: protect yourselves from opposing the Book of Allah.
[156] This is a refutation of the first excuse — referring to two groups: the Jews and the Christians, to whom the Torah and the Gospel were revealed.
Their excuse was: We were unaware of what they read.
There were two reasons for this:
1. The language of the scriptures was non-Arabic — either Syriac or Hebrew — and the Arabs did not understand those languages.
2. They (the People of the Book) used to conceal the scriptures and did not explain them to the common people.
[157] This is a refutation of the second excuse, and it is also found in verse 42 of Surah Fāṭir.
Before (taqūlū), according to the Basri grammarians, the implied word is karāhiyyah (dislike), and according to the Kufans, it is li-alla (so that not).
(Lakunnā ahdā minhum) — this was the claim of the Arabs, because they saw themselves as highly intelligent, sharp-minded, thoughtful, and inclined toward reflection.
After (wa raḥmah), the phrase "then you denied" (kadhabtum) is implied.
(Wa ṣadafa ‘anhā) — the verb ṣadafa can be both intransitive (to turn away) and transitive (to prevent others). Ibn Kathīr favors the transitive meaning here: they prevent others from it (the Qur’an).
Then comes a warning for those who turn away from the Qur’an — this turning away is a cause of punishment, which is why it is repeatedly emphasized.